In the related art, a spectroscopic device for measuring characteristics of materials using electromagnetic waves such as ultraviolet rays, infrared rays, microwaves, and terahertz waves is known. Spectroscopy is classified into absorption spectroscopy or emission spectroscopy depending on a physical amount measured by electromagnetic waves. In the absorption spectroscopy, electromagnetic waves transmit through a sample as a spectroscopic measurement target, so that physical or chemical properties of the sample are measured on the basis of a change of the electromagnetic wave caused by interaction between the electromagnetic wave and the sample during transmission through the sample. Meanwhile, in the emission spectroscopy, electromagnetic waves are emitted from the sample in any method, and the intensity of the emitted electromagnetic wave is measured.
A measurement target substance used as a sample of the spectroscopic measurement encompasses various types such as a gaseous type, a solid type, and a liquid type. A method of installing the measurement target substance has been studied in order to allow electromagnetic waves to appropriately transmit depending on each type. For example, in order to perform high precision measurement for the liquid type sample, it is necessary to form the sample arranged on the spectroscopic device to be thin enough to transmit electromagnetic waves. In particular, when the liquid sample is subjected to the spectroscopic measurement based on terahertz waves, an absorption effect of the terahertz wave caused by water molecules is strong. Therefore, in order to prevent degradation of an S/N ratio of the measurement signal, it is necessary to shape the liquid in a plate-shaped uniform thickness membrane and allow terahertz waves to transmit through the plate-shaped portion to perform measurement.
In general, in the measurement of the liquid sample, a sample is nipped into a container (usually called a “liquid cell”) formed of a material capable of transmitting electromagnetic waves, such as glass, and electromagnetic waves are incident to the liquid cell from the outside, so that the electromagnetic wave transmitting through the liquid cell is measured. However, when the measurement is performed by nipping the liquid sample into the liquid cell, spectrometric information on a cell material is mixed as noise with the spectrometric information on the liquid sample, and this hinders measurement of genuine spectrometric information.
In the related art, in view of such problems, a device capable of measuring spectrometric information with little noise without using the liquid cell has been proposed (for example, refer to Patent Documents 1 and 2). In the devices discussed in Patent Documents 1 and 2, a thin plate-shaped liquid membrane is formed by jetting the liquid sample from a nozzle having a special structure by a pump pressure.
However, if the liquid is pressurized by the pump and is jetted from the nozzle, the liquid may be dispersed from a nozzle opening. This dispersed liquid may pollute an optical system disposed near the nozzle disadvantageously. Note that it is necessary not to place any material other than the measurement target liquid in a portion where electromagnetic waves transmit through a liquid membrane formed by the nozzle. For this reason, it is difficult to enclose the vicinity of the nozzle in a closed space and provide a wall for perfectly blocking the dispersed liquid.
It is conceived that the liquid dispersion in the nozzle opening is generated by air bubbles contained in the jetted liquid. That is, in a case where the measurement target liquid jetted from the nozzle is stored in a recovery reservoir and is circulated using a pump in use, the liquid pressurized and jetted from the nozzle rebounds from a surface of the stored liquid and generates dispersion when it enters the recovery reservoir. In this case, the liquid stored in the recovery reservoir generates air bubbles due to agitation. In addition, the liquid containing the air bubbles is sucked using a pump and is pressurized again. Then, the liquid is sent to the nozzle. The air bubbles contained in this liquid cause bumping in the nozzle orifice and thus generate dispersion of the liquid.
A technique of preventing dispersion of water discharged from a water jet nozzle has been proposed (for example, see Patent Document 3). In the technique of Patent Document 3, a flow path expansion portion is formed in an upper surface side of a water channel directed from a water supply source to the water jet nozzle, and the air contained in the air bubble mixture water is selectively delivered to the upper wall surface of the flow path expansion portion and then collides with a step formed in a flow path narrowing portion directed from the expansion portion to a normal portion so that the air bubbles are fragmented or eliminated. As a result, it is possible to prevent dispersion of water discharged from the water jet nozzle.
Patent Document 1: JP-A-2011-127950
Patent Document 2: JP-A-2015-219088
Patent Document 3: JP-A-2005-213880